The goal of this application is to build a cell-flow/laser flash photolysis apparatus for the measurement of receptor function directly on the surface of a single cell with a microsecond-to- millisecond time resolution. a technique with such a time resolution has not been available. The apparatus will consist of several attached parts: (1) Cell-flow device with a 20-millisecond time resolution for applying photolabile neurotransmitters to a single cell. (2) Whole-cell current recording apparatus, with associated computing, for recording and analyzing the whole-cell currents that are induced by the applied neurotransmitter. (3) Laser and associated optics for (a) determining the rate of photolysis and quantum yield of the photolabile compound, and (b) removing the photolabile protecting group and, thereby, releasing the neurotransmitter, which binds to its specific neurotransmitter and induces the flow of currents across the cell surface. Neurotransmitter release has a time resolution of 200 microseconds. The measurements can be made with any cell that carries receptors for acetylcholine, GABA, glycine, glutamate, aspartic acid, or N- methyl-D-aspartate. We have made photolabile precursors of all these compounds.